The present invention relates to a method of activating thiourea dioxide.
Thiourea dioxide is also called formamidine-sulfinic acid or aminoiminomethanesulfinic acid and is often abbreviated as TDO or TUD.
Thiourea dioxide is a powdered stable compound, which dissolves in water and decomposes gradually to exhibit a reducing action. But, this reaction is slow, and particularly in an acidic to weakly alkaline region thiourea dioxide is stable and its reducing action is weak.
Usually, thiourea dioxide dissolves in water and produces sulfoxylic acid through formamidine-sulfinic acid. This reaction is promoted by the application of heat or in the presence of an alkali, and a strong reducing action is thereby exhibited. ##STR1##
The only method for promoting the reaction in an acidic to weakly alkaline region is to raise the temperature. In the case where raising the temperature is restricted for some reason, it has heretofore been unavoidable for thiourea dioxide to be used in an uneconomical state in which it cannot fully exhibit its effect. Further, also in the utilization of thiourea dioxide in an alkaline region, although thiourea dioxide produces a very stable sulfoxylic acid, its sulfoxylic acid producing speed is slow as compared with sodium hydrosulfite (hereinafter referred to simply as "hydrosulfite") which is a reducing agent in wide use, so when it is desired to utilize a quick effect in a short time, it has heretofore been impossible for thiourea dioxide to fully exhibit its reducing power latent therein.
Thus, heretofore there have been many cases where thiourea dioxide cannot fully exhibit its reducing power. But, there are various uses thereof. For example, in the textile industry, it has been utilized as a reducing agent for vat dye (see (U.S. Pat. Nos. 3,104,150 and 3,077,370 and Japanese Patent Publication Nos. 37630/1980, 37631/1980, 37632/1980, 37633/1980, 37634/1980, 37635/1980 and 5904/1982), further utilized for discharging of printed cloth (see German Pat. No. 941,363), bleaching of protein fibers (see Japanese Patent Publication No. 15648/1968), shrink proofing (U.S. Pat. No. 3,049,445) and reduction clearing of cloth dyed with disperse dye (see Japanese Patent Publication No. 27277/1977); in the paper pulp industry it has been utilized for bleaching of wood pulp (see U.S. Pat. Nos. 2,860,944 and 3,384,534 and British Pat. No. 1,079,135); in the photographic industry, as an auxiliary agent of developer (see Belgian Pat. No. 547,323 and German Pat. No. 942,777); in the cosmetic industry, as an auxiliary agent for hair waving (see German Pat. No. 1,083,986). Such uses as a reducing agent for high polymer polymerization (see U.S. Pat. Nos. 3,344,128 and 3,060,142), a detergent composition (see Japanese Patent Publication No. 3811/1974) and a precipitant for heavy metals in water (see Japanese Patent Publication No. 12188/1976) are also known.